hey, i've just finished maths in y12, did a full a level paper for mocks and got A* predicted so hopefully i can be of some help! but basically i would just recommend lots and lots of practice questions, that's quite obvious but realistically that's the only way - every time you learn a topic do as much practice as you can get, eg. use mathsgenie questions, or physics and maths tutor exam questions, madas maths is also super helpful as there are LOADS of questions on there, and the A level maths revision website is absolutely amazing (
https://alevelmathsrevision.com/). i always did physics and maths tutor and A level maths revision website questions and that really enhanced my abilities, madas maths has lots so I would pick out the best questions and use those.
before my mock exam, seems obvious but i just did as many past papers as possible because schools tend to use papers from real A levels (eg. my school used 2023 papers for my 2024 mocks because we couldn't access these yet). but point is, if you do lots of past papers, you get a feel for the format, and each paper from year to year isn't massively different. honestly if you do all the past papers you will be very well prepped.
for mechanics in particular i used this textbook
https://www.amazon.co.uk/Edexcel-Mathematics-Statistics-Mechanics-Textbook-ebook/dp/B07LH5JV4Y and just did lots of questions from this which helped a lot.
for statistics the questions get quite repetitive like there's only so many questions that can be asked, so if you do textbook questions (from the same textbook as for mechanics, those are good) and other practice questions which I said, you should be fine
tbh don't stress too much, maths is fine as long as you put in the effort you'll be great! good luck